BME 130 – Genomes

Lecture 23

Genome evolution I:

Mutations, repair, and recombination

TransitionsA GC T

TransversionsA CA TC GT G

When and how do mutations

happen?

DNA polymerases are not perfect:DNA polIII error rate =~ 1 x 10-7

Minimizing polymerase error

Polymerase slippage leads to indels

Slippage can get progressively worse

Mutagens and other -agens

Chemical mutagens

Figure 16.6a Genomes 3 (© Garland Science 2007)

(nitrous acid)

Physicalmutagens

UV radiation

Abasic site

Consequences of mutations

Mutations in gene sequence

Figure 16.12 Genomes 3 (© Garland Science 2007)

Figure 16.13 Genomes 3 (© Garland Science 2007)

Figure 16.14 Genomes 3 (© Garland Science 2007)

DNA repair

Minor pathway

Recognizes distortion of DNA

double helix

Similar concept for eukaryotes;

TFIIH helicase is used;

transcription coupled repair

Base mismatch: who is right?

DNA break repair

SOS!(why only in bacteria?)